Ah, making heavy cream from milk is a handy trick! You can combine 2/3 cup of whole milk with 1/3 cup of melted unsalted butter. Blend them until smooth, and you'll have a substitute for 1 cup of heavy cream. It's quite convenient when you're in a pinch. Have you tried making cream this way before, or are you planning to use it for a specific recipe? I'd love to hear about what you're cooking up!